HOLLYWOOD, Fla. — While Donald Trump works to build bridges with the Republican insiders who could decide a deadlocked convention, an anti-Trump group is racing to keep the two camps apart.

Our Principles PAC, an outside group devoted to defeating the billionaire, will be appealing to Republican National Committee officials gathered here for the party’s annual spring meeting. The super PAC, led by Republican strategists Brian Baker and Katie Packer, is presenting the committee’s 168 members — all of whom will be delegates at the July convention in Cleveland — with a four-page memo arguing they should reject calls to unify around Trump.

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The offensive comes at a perilous time for the “stop Trump" movement. Following Trump’s landslide win in New York, where the anti-Trump forces barely competed, there is a growing sense that he has seized momentum in the primary contest after a rocky period of internal disarray and a loss to Ted Cruz in Wisconsin. Trump is also expected to win all the states in contention next week.

Looking to exploit their newfound strength, Trump’s top brass — including strategists Paul Manafort and Rick Wiley — met with RNC members on Thursday. During a presentation lasting more than one hour, they laid out the case for why Trump would be able to defeat Hillary Clinton in a prospective general election matchup. They also sought to reassure the RNC — which Trump has repeatedly lambasted, accusing it of orchestrating an unfair nomination process that’s stacked against him — that the mogul is interested in working with the party. After the meeting, some influential members emerged to say they were impressed.

On Friday, Our Principles PAC is looking to push back, telling RNC members that it’s not too late to stop Trump, who the group says would cost the GOP dearly in November.

“Over the course of the last few days, you have been bombarded with information, presentations, speeches from candidates and their surrogates and campaign staff urging you to support them in their quest to secure the Republican nomination for the presidency,” Packer writes in the memo. “Your job is a serious and important one. You are the elected leaders of this party, chosen by the Republican activists in your state to represent them at this meeting as well as the Republican National Convention in Cleveland.”

She adds: “For this reason I would like to make the case to you that the path to an open convention is still very clear and that, regardless of his current lead in the delegate count, Donald Trump should not be the Republican nominee for president.”

In a briefing with reporters here, Packer acknowledged that some in the party are eager to unify around Trump following a prolonged and bitter primary season. But she said she would urge RNC members to fight the mogul all the way to an open convention.

She said her group plans to do its part and that it would soon roll out aggressive anti-Trump campaigns in Indiana and California, perhaps the two most critical states remaining in the primary calendar. It will also be investing in next week’s Maryland primary, where it’s spending more than $200,000, according to data provided by The Tracking Firm, a group monitoring media buys.

“There’s pressure from the media and certainly the Trump campaign to rally around Trump as the nominee,” Packer said. “What is the pressure to rally around a guy who has a minority of support?”